1. Field of the Invention
The present invention relates to a compact drive apparatus for driving an information record medium, such as a hard disk drive.
2. Description of the Related Art
Conventionally, a data recording and reproducing apparatus, e.g., a hard disk drive (hereinafter referred to as HDD), is provided with a spindle motor as a drive mechanism for rotating a disk. It is generally known that a drive mechanism of a radial or axial type is used for this purpose.
An example of the axial-type drive mechanism is disclosed in U.S. Pat. No. 4,658,312. This mechanism comprises a rotating shaft, rotatably supported by a bearing tube through a pair of bearings, and a rotor casing fixed to the shaft. The disk is supported by means of the rotor casing. A coil serving as a stator is fixed to the outer circumferential surface of the bearing tube, and a ring-shaped magnet is fixed to the inner circumferential surface of the rotor casing. The coil and magnet extend in the axial direction of the rotating shaft. The magnet is situated outside the coil and faces thereto. The rotating shaft and the rotor casing are rotated by the interaction between the magnetic field generated by magnet and the current flowing the coil. In this case, the magnetic field acts on the coil in a direction perpendicular to the rotating shaft, i.e., in a direction parallel to the surface of the disk.
An radial-type drive mechanism comprises a ring-shaped magnet fixed to a rotating shaft, and a coil arranged to face the magnet. The magnet and the coil extend in a direction perpendicular to the rotating shaft, i.e., in a direction parallel to the surface of the disk. The magnetic field generated from the magnet acts on the coil in the axial direction of the shaft.
The miniaturization of HDDs has recently been accelerated, and disks of small diameters, e.g., 2.5 inches, have been coming into wide use. Accordingly, in order to miniaturize HDDs, it is required to miniaturize not only the disk and but also the disk drive mechanisms.
The HDDs may be miniaturized by two methods. According to one method, the radial length of the disk and the mechanism is curtailed to reduce the plane area thereof. According to the other method, the axial length of the mechanism is lessened to lower the profile thereof.
In the aforementioned axial-type drive mechanism, however, if the axial length of the rotating shaft is decreased in order to reduce the thickness of the HDD, the axial length of the coil and the magnet is also decreased. As a result, the area of the magnet facing the coil decreases and a necessary driving torque can not be obtained.
In the radial-type drive mechanism, if the radial length of the disk and the mechanism is reduced in order to decrease the plane area of the mechanism, the radial length of the coil and the magnet is also reduced. Thus, the area of the magnet facing the coil decreases and a necessary driving torque can not be obtained.
Due to the reason described above, the HDDs cannot be easily miniaturized or thinned.